1. Field of the Invention
The invention relates to an authentication-encryption unit and an authentication-decryption unit and an associated method.
2. Discussion of the Background
An encrypted exchange of data via a common medium, such as the Internet, without the need to allow unauthorized access to the data to be transmitted (confidentiality protection) is of great importance. In addition to a sufficiently high level of encryption, it is also important that the integrity of the data transmitted is secured in order to guarantee that the data transmitted has not been altered on the transport route. An integrity protection of this kind is achieved, for example, by forming and also transmitting a checksum over the transmitted encrypted data.
A device and a method, with which a datastream is subdivided into individual blocks, wherein the individual blocks are encrypted and wherein a common checksum is calculated over the individual encrypted data blocks, are known from DE 10 2008 013 785 A1. A method known as the “Galois Counter Mode” and published by the National Institute of Standards and Technology (NIST) is used for this purpose. This published method is adopted in full into the present description through referencing.
The disadvantage with DE 10 2008 013 785 A1 is that it is not possible to remove individual encrypted data blocks or individual bits in the individual encrypted data blocks from the formation of a checksum. However, especially in the case of real-time applications, such as language transmissions, image transmissions or video transmissions, this is particularly desirable. If a transmission error occurs in the transmission of encrypted language, image or video data and, for example, one bit is transmitted incorrectly, this error is noticeable only marginally if at all through the absence of a checksum. If a checksum is calculated over the encrypted data blocks, the entire packet is rejected in the event of an incorrect transmission of one bit; this is associated with considerable disadvantages, especially in the case of the above named real-time applications, and has very disturbing effects. The user's “Quality of Experience” is reduced.